Integrating natural baselines into ecosystem restoration: scaling herbivore targets for European landscapes

Abstract

Abstract Introduction Herbivore‐mediated ecosystem processes are fundamental to biodiversity, yet have been greatly diminished by megafauna extinctions and replacement of wild herbivores by managed livestock. With increasing restoration ambitions—including the United Nations' (UN) Decade on Ecosystem Restoration and the European Union (EU) Nature Restoration Law—there is a need to set meaningful restoration targets for large mammalian herbivores. Objectives We quantify natural baselines for herbivore biomass and body‐size structure and describe the roles of predation and migration. We also propose a dual framework of baseline‐aligned targets and partial restoration targets to support restoration planning. Methods At a workshop, we identified the biomass, size distribution, predation, and migration of large herbivores as key elements of a natural baseline. We synthesized paleoecological evidence, data from near‐intact ecosystems, and rewilding projects to provide empirical estimates of biomass and size structure. Results Based on paleoecological and near‐intact ecosystems, we tentatively set natural herbivore biomass at approximately 5000–30,000 kg/km 2 , with small herbivores (10–100 kg) contributing approximately 5–10% of total biomass and large and megaherbivores (≥500 kg) approximately 60%. Current European reserves average just 800 kg/km 2 —an order of magnitude lower—and are strongly skewed toward small and mesoherbivores such as deer and wild boar. Conclusions Given current constraints, these targets are unlikely to be fully met. Partial restoration, however, will improve ecosystem processes and likely biodiversity, but knowledge gaps remain, including how deviations from natural baselines affect biodiversity.